1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, it relates to write-in and readout of data with respect to a memory unit of a replacement part detachably installed in an image forming apparatus.
2. Description of the Related Art
Some kinds of an image forming apparatus, such as a printer, a duplicator, a digital composite machine and a facsimile machine, have a replacement part detachably installed therein, examples of which include a toner cartridge and a photoreceptor drum cartridge. It has been practiced that the replacement part is provided with a nonvolatile storage medium, which stores management data, such as an enumeration data indicating a consumed amount of the replacement part (such as a number of sheets consumed for printing) and user information, and the management data stored in the nonvolatile storage medium is read out from and written in the image forming apparatus main body.
In the case where the stored contents of the nonvolatile storage medium of the replacement part are falsified, such a problem occurs that, for example, a replacement part having been deteriorated in quality due to excessive use beyond the prescribed service life is utilized by installing in an image forming apparatus. In such a case, not only printouts with high quality cannot be provided, but also there is such a possibility that the image forming apparatus itself is damaged. Consequently, it is necessary to detect falsification of the data stored in the storage medium of the replacement part.
JP-A-2001-209580 discloses a technique for detecting falsification, in which an authentication process is executed upon reading and writing data on the storage part to prevent the data from being read out and written in by a false third party. In this technique, furthermore, after writing the data, an encrypting process is executed based on the written data, and the result of the encrypting process is verified to validate the written data.
JP-A-11-53487 discloses a technique for improving fastness to breakage and falsification, in which same data are written in plural locations of an embedded memory of an IC card, and upon readout, the data stored in the plural locations are read out to determine the correct data by majority decision.
However, in the case where the technique disclosed in JP-A-2001-209580 is applied to a storage device of a replacement part of an image forming apparatus, it is necessary to provide a mechanism for the authentication process in the storage device, which raises the production cost. In the technique disclosed in JP-A-11-53487, the correct data is determined by majority decision of the data stored in the plural locations in the memory, and therefore, it has such a problem that in the case where false data is written in majority of the locations, the false data is judged as correct data to overlook falsification.